Polyol ethers, such as glycerol ethers, glycol ethers and polyglycol ethers, are well established materials that find widespread use in industry and in consumer products, including as solvents, surfactants, wetting agents, emulsifying agents, lubricants, and intermediates for the preparation of surfactants.
Glycol and polyglycol ethers are typically produced by catalytic alkoxylation of glycols or polyglycols with alkylene oxides such as ethylene oxide. However, there are significant disadvantages to this process, including the difficulty of stopping the reaction after one molecule of alkylene oxide has added to one alcohol group of the glycol or polyglycol. Instead, it is typical for the reaction to continue proceeding, undesirably resulting in a molecular weight distribution of products.
The conventional preparation of glycerol mono-ethers, as an example of other polyols, is a three-step process requiring: (1) protecting glycerol with acetone to form solketal (4-hydroxymethyl-2,2-dimethyl-1,3-dioxolane), (2) reacting solketal with bromoalkanes in a strong alkali solution preferably in the presence of tetrabutylammonium bromide as a phase transfer catalyst, and (3) hydrolyzing the ketal protection with hydrochloric acid (see Queste et al, Green Chem. 2006, 8, 822-830). The process has several disadvantages, including that it involves three overall steps, generates large amounts of inorganic salts, and provides low product yields. Further, the process has not been demonstrated suitable for use with secondary alkyl bromides, thus limiting the structural diversity of potential products.
U.S. Pat. No. 5,446,210 describes a process for the production of polyol ethers by reacting a polyol and a carbonyl compound with hydrogen in the presence of a hydrogenation catalyst. A molar ratio of polyol to carbonyl compound of 5:1 to 1:5 is described, although a ratio of 1:1 to 1:4 is taught as preferred (also, all of the examples were conducted with an excess of carbonyl compound). One of the shortcomings of the '210 patent's process is the low yield of etherified polyols. For instance, the reference indicates total ether (mono and bis) yields of 35 to 50%. In addition to the low yields, the process exhibits low selectivity for the mono-ether product over the bis-ether product, as demonstrated in the reference's examples.